This invention is directed to the problem of transmitting varying types of data over a single communication path.
The ability to transfer data from one point to another is fast becoming the backbone of our industrialized society. As data transmission becmes more and more popular the level of sophistication required also rises. Thus we find a situation developing wherein, especially in the business environment, any terminal connected to the switching network must be capable of handling any type of data presented to it in an efficient and universal manner.
While such remains the goal, the problem is compounded in that the data from differing types of equipments arrive at the data terminal in differing forms and at differing rates. For example, data which is representative of speech is usually continuous in nature, For this reason it follows that when voice data is being transmitted it is necessary to establish a continuous or "circuit switched" connected through the network. On the other hand data from a computer terminal or from a sensing device, arrives in spurts and is thus "bursty" in nature. Such bursty data must be immediately forwarded when it appears at the terminal, but due to its bursty or noncontinuous nature many such independent bursty data inputs may be interleaved in a given period of time.
One arrangement for controlling a plurality of data inputs over a common communication channel is to buffer the various data inputs an then statistically multiplex the various buffered inputs so as to communicate over the transmission link those inputs having full buffers. Typically this is accomplished by adding a header to each of the statistical samples transmitted over the link. Such an arrangement is satisfactory when all of the data inputs are bursty in nature since in such a situation natural gaps exist between the various data inputs allowing for a natural multiplex of the inputs. However, when an attempt is made to statistically multiplex communication links having continuous data, one of two problems arises. Either the buffer associated with the continuous data continues to saturate the channel thereby blocking all other buffers or, under some protocols, the continuous data would be ignored for certain periods of time while data from the other buffers is accepted. Both of these problems are intolerable in that to ignore bursty data is tantamount to losing that data. On the other hand, ignoring continuous data results in unacceptable delays and buffer overloading which causes distortion and loss of information.
It is well known to use a statistical multiplexer to solve the problem of communicating information from several bursty data inputs over a single communication link. One example of a statistical multiplexer can be seen in U.S. Pat. No. 4,082,922 (179-15). In C. R. Crue Case 1, U.S. Pat. No. 4,095,051, a demultiplexer is shown using a bit interleaved format. It is also known to utilize concentrators to select active ones of a number of lines under control of a remote controller for the purpose of communicating data over a single data link. In the Inose et al U.S. Pat. No. 3,790,715 there is disclosed a circuit for combining voice data and low speed data on a single line. Inose is an example of subrate multiplexing where the size of each data channel within a frame is adjusted to accommodate the anticipated size of each data word. In Inose, the data channels are permanently assigned, on a per call basis, to the data device. Inose does not take advantage of the bursty nature of some of the data and thus does not statistically multiplex the data.
Thus, while several techniques exist for combining bursty data inputs over a given telephone link, or for combining several continuous data inputs, the problem has remained as to how both such types of information inputs may be economically combined at a standard terminal and transmitted to a switching network over a single link.